JP Publication of Application No. 2001-325994 discloses a use of a managing device to monitor whether an article handling device is working normally. In such an article handling facility, by detecting any abnormal condition that has occurred in the article handling device, it is possible to take necessary measures, such as causing the managing device to command the article handling device to perform an operation in response to the abnormal condition, in order for the facility that includes such article handling device to return to the normal operations.
In order to keep track of the state of article handling devices at any time with a managing device, notifying information is transmitted from article handling devices to the managing device and is accumulated therein. Notifying information may, for example, be detailed information related to the operations of the article handing devices, and may, for example, be information generated based on state information, obtained at set time intervals, related to the state of the article handling devices. And the managing device determines whether an abnormal condition has occurred in an article handing device by analyzing the accumulated notifying information. By using the accumulated notifying information, the managing device can learn (i.e., be informed) not only the fact that the abnormal condition occurred in the article handing device but also the state of the article handling device at the time of the occurrence of the abnormal condition. Therefore, the managing device can learn of the nature of the abnormality by analyzing the circumstances under which the abnormal condition occurred in the article handing device. On the other hand, when the managing device analyzes the accumulated notifying information to detect presence of an abnormal condition and to learn of the nature of the abnormality, there may be a time lag between the time of the actual occurrence of the abnormal condition in an article handing device and the time at which the managing device learns of the nature of the abnormality.
In addition, since it is not possible to predict when an abnormal condition may occur in an article handing device, the article handling device must continue to send notifying information to the managing device while in operation. Therefore, there tends to be a large volume of communication traffic between an article handling device and the managing device, which may lead to congestion in the communication lines. Such condition becomes more prominent in a facility having a number of article handling devices. If the time intervals at which the notifying information is transmitted from the article handling devices to the managing device are made longer to reduce the frequency of communication, although this would reduce the communication traffic, the time lag before the managing device learns of the occurrence, and of the nature of, the abnormality would become even longer.